1. Field of the Invention
The present invention relates to a method for controlling product quality in a conversion of iron-containing feed material into a product useful in the direct conversion to steel. More particularly, the present invention relates to a method for insuring quality of the product by monitoring the composition of an iron carbide-containing product and adjusting process parameters in direct response thereto.
2. Description of the Related Art
The steel industry has relied on a process that has been in use for many years for the conversion of iron ore into steel. This process involves the conversion of iron ore to pig iron in a blast furnace using coke produced in a coke oven and the subsequent conversion of the pig iron or hot metal to steel in an open hearth or basic oxygen furnace. Though relatively simple, this method has a number of drawbacks, some of which have become potentially devastating to the steel industry in recent years. First, the traditional process of producing steel is energy intensive. With the cost and availability of energy in the near future being unpredictable, the traditional manner of producing steel faces an uncertain future. Second, environmental standards now in place in most industrialized countries make the construction of new traditional-style steel mills impractical. To build such a plant to meet pollution standards or to modify an existing plant to meet the standards would be so expensive as to render the cost of the steel produced non-competitive.
Accordingly, in recent years, a demand has been created for new, relatively clean, energy efficient and less expensive methods for producing steel. In this regard, a great deal of effort has been directed to the elimination of the blast furnace and the coke oven in the steel-making process. Blast furnaces and coke ovens are inherently inefficient, requiring large quantities of energy, and are responsible for a large portion of the pollution from a traditional steel mill. One possible technique that has been studied involves the direct conversion of iron-containing materials to iron carbide followed by the production of steel, thereby eliminating the blast furnace in the production of steel.
Stephens, Jr. U.S. Patent No. Reissue 32,247 discloses such a process for the direct production of steel. In this process, iron ore is converted to iron carbide, Fe.sub.2 C and/or Fe.sub.3 C, and the iron carbide is then converted directly to steel in a basic oxygen furnace or an electric arc furnace, thereby eliminating the blast furnace step altogether. The key to this process is the conversion step, in which iron oxide in the iron ore is reduced and carburized in a single operation using a mixture of hydrogen as a reducing agent and carbon-bearing substances as carburizing agents.
While this method of directly producing steel represents a significant advance in the art, improvements to the method are desirable. Further, a particular need exists for a technique for providing for the quality of the product. It has been found that even minor variations in the process parameters in the converting step will cause undesired results, and that the required parameters are difficult to maintain. Even a minor variation from the appropriate process parameters can cause free carbon (C), free iron (Fe) and/or iron oxides such as Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4 or FeO to be produced rather than iron carbide.
A need clearly exists for an improved conversion method and a method of controlling the conversion and insuring that the final product is acceptable.